package com.SuanFa.mati;

import java.text.DecimalFormat;
import java.util.Arrays;
import java.util.Scanner;

//有缘的竹鼠
public class ccc {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int L = sc.nextInt();
        int [] nums = new int[n];
        for (int i = 0; i < nums.length; i++) {
            nums[i] = sc.nextInt();
        }
        Arrays.sort(nums);
        int temp = 0;
        for (int i = 1; i < nums.length; i++) {
            int nu = nums[i]-nums[i-1];
            temp = Math.max(nu,temp);
        }
        double temps = (double) temp /2;
        temps = Math.max(temps,nums[0]);
        temps = Math.max(temps, L - nums[nums.length-1]);
        DecimalFormat df = new DecimalFormat("#0.00"); // 定义格式
        String formattedNumber = df.format(temps); // 格式化数字
        System.out.println(formattedNumber); // 输出: 123.40
    }
}
